Police officers in Manchester and elsewhere will discuss specific deployments with their military regional counterparts. The soldiers will be in uniform but under the command of the police. Ewen MacAskill

Almost 1,000 troops will be deployed to Britain streets after the threat level was raised. About 984 troops will be stationed from Wednesday, replacing police guards at No 10 Downing Street, parliament and Buckingham Palace, and elsewhere around London. The changing of the guard ceremony at the palace has been cancelled.

Police named the suspect as Salman Ramadan Abedi, 22, who they said was born in Britain and was from a Libyan background. He has not been formally identified by the coroner. A 23-year-old man arrested on Tuesday is believed to be Ismail Abedi, the brother of the suspected bomber. He is still being questioned.

Three men have been arrested in south Manchester in connection with the investigation into the attack, Manchester police have announced.

Officers said 59 people were hospitalised and 60 treated by paramedics at the scene following the explosion, which hit the venue shortly after the concert finished. Twelve of those taken to hospital were aged under 16, North West ambulance service said.

Who was responsible?

The police say they believe the attacker was carrying an improvised explosive device, which he detonated.

Multiple witnesses said they heard an explosion, with one telling the Guardian the blast shook the building, before “everyone screamed and tried to get out”.

A 23-year-old man was arrested on Tuesday morning in south Manchester, the police said. The Arndale shopping centre was evacuated and a man was arrested there but this was unconnected to the attacks, the police said.

Armed police carried out a controlled explosion at a house in Fallowfield and raided a block of flats in Whalley Range, both in south Manchester, on Tuesday morning as part of the investigation into the attacks.

Where did it happen?

Manchester Arena said the incident took place “outside the venue in a public space”.

The blast was reported to have hit the foyer of the building at about 10.30pm, British Transport police said.

Victims have been taken to eight hospitals across the Manchester area.

Large parts of the city around the arena have been sealed off. Victoria station has been closed and is expected to be closed throughout Tuesday.

Police have asked the public to avoid Manchester city centre on Tuesday as they continued to work in the area. Some roads in the city centre have been closed for much of the day and public transport has faced disruption.

Police carried out a controlled explosion in the Cathedral Gardens area but the item destroyed was not suspicious.

How did Theresa May react?

Theresa May has said her thoughts were with the victims and families of those affected in “what is being treated by the police as an appalling terrorist attack”. In a televised appearance outside 10 Downing Street, she attacked the “appalling, sickening cowardice” of the bombing.

Other reactions

The home secretary, Amber Rudd, described the bombing as a “barbaric attack” that targeted “young people, children out at a pop concert”.

May chaired two meetings of the Cobra government emergency committee. She also travelled to Manchester to meet the chief constable, mayor and emergency services, she said, and visited Manchester children’s hospital.

The Queen issued a statement condemning the “act of barbarity”, offering her sympathies to those affected and thanking the emergency services. “The whole nation has been shocked” by the attacks, she said.

The Labour leader, Jeremy Corbyn, and the Liberal Democrat leader, Tim Farron, have expressed their sympathies for the victims.

General election campaigning has been suspended.

The US president, Donald Trump, gave a statement from his trip to Israel in which he called the attackers “evil losers”. Trump spoke to the prime minister to offer US assistance in the investigation into the attack and assuring her that “Americans stand with the people of the United Kingdom”, according to a read-out of the call.

The London mayor, Sadiq Khan, condemned “barbaric acts of terrorism”.

Police reaction

The Metropolitan police said it asked for soldiers to be sent on to the streets in order to free up armed officers currently deployed on guard duties.

The force’s commissioner, Cressida Dick, said additional police would be on duty in London throughout the weekend.

Police urged those who are concerned about loved ones who were in the area to call the National Casualty Bureau on 0800 096 0095 (+448000960095).

Police have issued an urgent appeal for anyone who was in the city centre between 8pm and 11pm on Monday night and has dashcam footage to submit it to the National Police Chiefs’ Council image appeal site.